This invention relates generally to the construction of golf balls, and more particularly to a ball construction characterized by multiple concentric sections, including an innermost section consisting of essentially non-compressible material allowing variations in the radial dimensions and densities of outer sections to permit control variations in spin rate of the ball.
Historically, golf balls have been produced utilizing a one-piece or unitary construction, a two-piece construction, which incorporates a solid core, and a separate cover, or three-piece construction, which is comprised of a solid or liquid-filled center, which is covered with rubber thread windings or a solid rubber shell, and finally, a cover material. The one-piece, two-piece and three-piece ball constructions have different radii of gyration, and hence different spin rates when struck by a golf club. The closer the radius of gyration is to the center of the ball, the greater the spin rate of the ball. Hence, three-piece golf balls, with a heavy solid or liquid-filled center, and the very light density created by the air spaces between the rubber thread windings, spin considerably more than solid or two-piece construction balls.
It has long been desired to be able to adjust the spin rate of the golf ball. This feature would allow the designer to design the ball for the greatest distance or for the greatest "bite" on the green, while not requiring a change in the cover material of the ball. With existing construction materials, the designer has had very little freedom to substantially change the spin rate of the ball, and the small changes, which could be made, required that substantial and often detrimental material changes be incorporated. As an example, it is known that softer cover materials will produce more spin, but only at the expense of the initial velocity of the ball.
Even the latest solid construction three-piece balls, with a solid rubber center, a solid rubber shell of a different density around the center, and finally a cover of a third density, do not allow for substantial adjustment of the spin rate of the ball, due to the fact that the polybutadiene rubber, which is used for the construction of the center and rubber shell, has a density of about 1.1 with no filler, and performance diminishes substantially if filler is added to the compound. Further, the ball performs best when the rubber material with no filler is closest to the cover of the ball. This means that, while the spin rate can be somewhat controlled, there is not a great deal of flexibility afforded the designer.